Objects such as spar chords, which are essentially the frame of an airplane wing, are measured to ensure that the dimensions of the object meet certain threshold requirements. In the case of spar chords, achieving these dimensions assist in providing airplane wings that will withstand the elements associated with flying.
Spar chords can be sixty (60) to one hundred (100) feet in length and can have angled shaped parts that form the four (4) corners of a wing box. FIG. 1 depicts a spar chord 100 supported by saw horse devices 102. There can be, for example, a total of eight (8) spar chords per airplane. Spar chords typically can vary in five basic cross-sectional dimensions as shown in FIG. 2.
The first dimension of the spar chord 100 is the base which has a length “A”. The second dimension is the thickness of the base “B”. The spar chord 100 has a component that extends upward from the base which has a vertical height “C” (the third dimension) and a thickness “D” (the fourth dimension). The fifth dimension is the “angle” formed between the base and the component extending upward from the base. In practice, these five (5) basic dimensions can have, for example, up to 11 variations or more that are not consistently defined on all plane models.
It is necessary to measure up to 300 features on each part. Each feature is defined as a transition point. The measurement requirement is generally two fold. First, the length portion of the transition is located and then second, the cross section is measured. Complicating the problem of measurement is that a large percentage of the transitions in the cross-section are so gradual that the transition point is often obscured by surface roughness introduced in hand finishing operations. The requirement to locate the transition point of a feature dictates that many points in the region of the transition must be measured. A sufficient number of points must be measured before and after the transition to accurately calculate the transition portion.
Hand tools as depicted in FIG. 3 have been used to measure dimensions of a spar chord. In order to determine if a spar chord meets certain dimensional criteria, a steel tape is stretched along the length of the spar chord and is clamped at both ends. A part drawing along with a Quality Assurance Inspection Plan (QAIP) are typically utilized to determine which part of the spar chords need to be measured and tolerance ranges for each measurement. `This is done manually by locating specified transitional positions, referred to as “dollar sign” surfaces, on the base of the spar chord. These transitional positions are marked by hand down the entire length of the spar chord (could be from 60 to 100 feet). After the spar chord is marked, each marked transitional position is identified and matched up to the part drawing and correlated to the QAIP to determine which dimensions must be measured and the tolerance ranges the dimensions must fall within.
This method of part layout, manual measurement and manual comparison to a part specification is to some extent labor intensive and sometimes can present a flow bottleneck in a factory cell. Thus, it would be desirable to have an inspection system, apparatus and method for making such measurements.